1. Field of the Invention
The invention relates to an electric press machine which conducts press working on a lead frame in which pilot holes are formed while the lead frame is pitch fed to a press section having a press die. Also, the invention relates to a motor-operated press machine, and more particularly to a motor-operated press machine in which a press working operation with an ordinary stroke, and a die opening operation in, for example, replacement of a working die are enabled.
2. Description of the Related Art
A semiconductor device of the resin mold type is subjected to working such as dambar cutting and lead forming after resin mold working. These working operations are conducted by a press machine having a press die.
Usually, such a press machine is configured so that upper and lower dies are positioned between a punch holder which holds a punch, and a die holder which holds a die, and then set in the press machine, and press working is conducted while the upper die which is hydraulically or electrically vertically moved is guided by a guide post which is erected between the upper and lower dies.
As a mechanism for feeding a lead frame in such a press machine, the assignee of the present application has developed a machine disclosed in Japanese Patent Unexamined Publication No. HEI 6-77376. This feeding mechanism will be described. Referring to FIG. 1, at a press position, both the sides of a lead frame 101 are supported on feed plates 103a and 103b which are disposed above a die 102, respectively. The feed plates 103a and 103b are coupled to coupling members 104a and 104b. The feed plates 103a and 103b can be vertically moved by a vertically moving mechanism which will be described later. When the feed plates 103a and 103b are pressed down, the lead frame 101 is engaged with pilot pins 117 disposed on a die block 116, so as to be positioned. The reference numeral 118 designates a failure detecting pin which detects whether the lead frame is set at a predetermined position or not.
Feed pins 106a and 106b hang from the lead frame 101. The feed pins are caused to engage with pilot holes 101a of the lead frame 101 from the upper side, by feed arms 105a and 105b shown in FIG. 2. The feed arms 105a and 105b are reciprocated in the lateral directions in FIG. 2 by a reciprocating mechanism which is reciprocated by, for example, cylinder driving (an air cylinder).
The feed plates 103a and 103b are upward urgingly supported on rods 108a and 108b which are urged by coil springs 107a and 107a disposed on a pedestal section 107 shown in FIG. 3. The coupling members 104a and 104b are engaged with engaging members 109a and 109b. Lower ends of rods 110 and 110 respectively hanging from the engaging members 109a and 109b are linked in a vertically movable manner with rocking pieces 112a and 112a fixed to a rotation shaft 111. A rocking piece 112b is fixed to the rotation shaft 111. The cylinder rod of a cylinder 113 is coupled to the rocking piece 112b. When the cylinder 113 is operated, the rotation shaft 111 is rotated, so that the feed plates 103a and 103b are lowered against the urging force of the coil springs 107a, via the rocking pieces 112a and 112a, the rods 110 and 110, and the engaging members 109a and 109b.
In the press machine, when a feed cylinder which is not shown is operated and the lead frame 101 is fed by one pitch by means of the feed arms 105a and 105b, the cylinder 113 is operated to lower the feed plates 103a and 103b, thereby causing the feed pins 106a and 106b to disengage from the pilot holes 101a of the lead frame 101. Then, an electric motor or a hydraulic mechanism is operated so that an upper die section 114 is downward moved to a position where a stripper plate 115 presses down the feed plates 103a and 103b, thereby conducting press working. When the press working is ended, during a period when the upper die section 114 is upward moved, the feed arms 105a and 105b are moved to a position corresponding to the die 102, and wait there. The cylinder 113 is operated to upward move the feed plates 103a and 103b, thereby causing the feed pins 106a and 106b to engage with the pilot holes 101a of the lead frame 101 which is upward moved with being supported by the feed plates 103a and 103b. Then, the feed arms 105a and 105b are moved so as to feed the lead frame 101 by one pitch, and the above-mentioned press working is repeatedly conducted.
In the above-described press machine, the three kinds of operations, i.e., the vertical movement of the upper die section 114 by means of the electric motor or the hydraulic mechanism, the feeding operation of the feed arms 105a and 105b by means of cylinder driving, and the vertical movement of the feed plates 103a and 103b by means of the cylinder 113 are performed while they are synchronized with one other by electrical means. Therefore, press working of one cycle requires a prolonged time period (about 70 spm at the maximum), and it is difficult to shorten the cycle time (index time).
This is applicable also to a press machine in which the vertical movement of the upper die section 114 by means of hydraulic driving is employed. Since the number of parts is large, moreover, the production cost is high and the machine is bulky.
Since the feed arms 105a and 105b are fed by means of cylinder driving, the feeding is conducted at a constant speed. Therefore, a shock is applied to the lead frame 101 at the start of and before the stop of the feeding operation of the lead frame, and hence the lead frame is easily damaged. Furthermore, also the feed pins 106a and 106b are easily damaged.
The pitch of the pilot holes 101a of the lead frame 101 is varied depending on the kinds of the lead frame, and hence the stroke of the feeding to the press section must be adjusted. In the adjustment, the length of a stopper bolt or the like which regulates the range of the movement of the feed arms 105a and 105b due to cylinder driving must be adjusted. In order to adjust the feeding amount, it is necessary to stop press working, and hence the work efficiency is lowered.
When a lead frame is erroneously set, the operation of the press machine must be stopped, and the driving mechanisms for the upper die section 114 and the feed arms 105a and 105b, and the vertical driving mechanism for the feed plates 103a and 103b must be separately canceled. Thereafter, the lead frame is detached from the machine. In this way, the recovery work is cumbersome.
Also, in a motor-operated press machine of the crank press type, when a working die is replaced, for example, the bottom dead center of a press ram is adjusted so as to obtain a predetermined working accuracy. The bottom dead center of the press ram is adjusted in, for example, one of the following methods. A vertical movement shaft is threadably coupled to a slide, and the vertical movement shaft is rotated with respect to the slide, thereby adjusting the level of the slide (Japanese Patent Unexamined Publication No. HEI 5-123900). A crank shaft is configured so that its eccentric position is variable, and the adjustment is performed by adjusting the amount of eccentricity (Japanese Patent Unexamined Publication No. HEI 3-216296). The adjustment is performed by changing the position of a fulcrum of a rocker arm which pushes the ram (Japanese Patent Unexamined Publication No. HEI 4-157098).
In the case where, in a usual press machine, a working die is to be replaced, an upper die is removed from the press ram, the press ram is then moved above so as not to obstruct the replacing work, and the die is replaced. In a motor-operated press machine, the range of stroke of the press ram depends on the range of movement of the eccentric shaft of the crank. Hence, the range of stroke of the press ram is set to a relatively large value, and when the die is to be replaced, the replacing work is conducted after the press ram is moved to the uppermost position.
In such a motor-operated press machine of the prior art, the range of stroke for working is set as required for a press working operation. In replacement of the die or during maintenance, therefore, the die opening operation cannot be easily conducted. Furthermore, such a press machine has a structure in which, also in the case where the bottom dead center of the press ram is to be finely adjusted, the range of adjustment is small and therefore the adjustment cannot be readily performed.
Furthermore, the use of such a motor-operated press machine produces another problem in that, in the case where a trouble such as that a workpiece is erroneously fed to damage the die occurs during press working, it is impossible to immediately stop the press machine so as to prevent the die from being damaged. That is, when such a trouble occurs during press working, the press machine is stopped without delay to avoid a serious trouble. However, the inertia of the press ram or the like may make it impossible to immediately stop the press machine. In a resetting operation after jamming, correction cannot be manually conducted while inserting the operator's hand between the dies, with the result that the resetting operation requires a prolonged time period.
In order to solve these problems, the assignee of the present application has developed a motor-operated press machine disclosed in Japanese Patent Unexamined Publication No. HEI 8-150499.
In the motor-operated press machine, as shown in FIGS. 4 and 5, a press ram 114 is linked to a crank 120 which is rotated by a motor, thereby vertically reciprocating the press ram 114. A rocking link 126 is rockably supported on a supporting shaft 24 which is pivotally supported on a casing 112 disposed on a top plate 110 of the press machine. A crank shaft 122 which is a support shaft of the crank 120 is supported on one end portion of the rocking link 126. A driving rod 132 of an air cylinder 130 is engaged with the other end portion of the rocking link 126 which is on the opposite side with respect to the supporting shaft 124.
In a usual press working operation, as shown in FIG. 4, the air cylinder 130 upward extends the driving rod 132 so as to regulate the position of the rocking link 126 in an arrangement in which the crank shaft 122, the supporting shaft 124, and the press ram 114 are substantially on a straight line. The air cylinder 130 is pivotally supported on the casing 112 by a shaft 134 so as to be rotatable. Under this state, the one end portion of the rocking link 126 is located at a position which is in a further left side in FIG. 4 with respect to the vertical downward direction, and abuts against a stopper 36 attached to the casing 112. When the crank 120 is rotated about the crank shaft 122, the press ram 114 is vertically moved via a connecting rod 118 in which the upper end is coupled with an eccentric shaft 120a of the crank 120 and the lower end is coupled with the press ram 114, thereby conducting a pressing operation. The projection amount of the stopper 136 is adjusted by using an adjusting knob 138, whereby the bottom dead center of the press ram 114 can be adjusted.
In a resetting operation after jamming, an emergency during a working operation, or the like, as shown in FIG. 5, the driving rod 132 of the air cylinder 130 is retracted so that the rocking link 126 is rotated in a counterclockwise direction. This causes the press ram 114 to be upward moved to a position which is higher than that in a usual press working operation, so that the press ram 114 can be moved to a retracting position.
However, this motor-operated press machine has the following problem. Since, in a usual press working operation, the crank shaft 122, the supporting shaft 124, and the press ram 114 are arranged in a vertical direction so as to be substantially on a straight line as shown in FIG. 4, the casing 112 must have a large height. As a result, the total height of the motor-operated press machine and that of the press machine itself are increased.
In the case where, in order to move the press ram 114 to the retracting position in a resetting operation after jamming or the like, the press ram 114 is upward moved via the connecting rod 118 by rotating the rocking link 126, the crank shaft 122 through which the connecting rod 118 is coupled to the rocking link 126 is upward moved from a substantially directly below position in a vertical direction along an arcuate locus. When the press ram 114 is raised to some extent, the connecting rod 118 is laterally directed as shown in FIG. 5, with the result that the connecting rod 118 is raised from the lateral side. Therefore, a large force is required for the upward movement, so that a large air cylinder must be used as the air cylinder 130, thereby producing a problem in that the size of the pressing must be likewise increased.
When jamming or the like due to a failure in an operation of feeding a workpiece occurs during a pressing work, a large force is applied to the press ram 114. In a press working operation, as described above, the rocking link 126 is located at a position which is slightly deviated from the vertical downward direction, and the rotation of the rocking link is restricted by the stopper 136. Therefore, no escape for the force is provided. This causes a further problem in that there arises a trouble that the dies (a punch and dies) and the driving mechanism are damaged.